1. Field of the Invention
The invention relates to a network selecting scheme and, more particularly, to a method and system for selecting an access network in a heterogeneous network environment.
2. Description of Related Art
Since current heterogeneous access networks typically have features respectively, it is a very important target that a mobile user can obtain the best quality of services (QoS) on mobile communications by means of the features. For example, the series of wireless local area network (WLAN) IEEE 802.11 generally has a high transmission rate but a very small covered area. By contrast, other networks like General Packet Radio Service (GPRS) and Universal Mobile Telecommunication (UMTS) have a low transmission rate but a wide covered area. Accordingly, when the mobile user is roaming between the networks with different features, the change of transmission rate is approximately 100 times, which greatly affects the QoS.
U.S. Pat. No. 6,282,577, titled “Mobile Terminal and Method for Controlling Network Connection Thereof”, describes a control scheme for detecting an existing network and its connection. Accordingly, a mobile device can automatically determine an ad-hoc network or a trunk network to connect, or alternately set an ad-hoc network to connect. In this patent, network IDs and types are applied to determine a current network to be connected to the mobile device based on a fixed priority sequence. In such a way, the QoS will be ignored and may select a network with poorer QoS.
In addition, the paper “Dynamic Adaptive Routing for Heterogeneous Wireless Network” issued in Proceedings of IEEE Globecom 2001, vol. 6, pp. 3608-3612, November 2001, by E. Wu, Y. Huang and J. Chiang, describes the Dynamic Adaptive Routing Protocol (DARP) for finding an optimal routing path in a heterogeneous wireless network, thereby obtaining the desired QoS. However, in such a way, the QoS is achieved by routing, which may spend more time.